He is a Facebook aficionado: Devoutly supported by young Muslims, al-Awlaki has exploited social networking to spread his teachings. He has groups on Facebook and MySpace and his “fans” include American high school students.

He hasn't always preached extremism: In the weeks after 9/11, al-Awlaki spoke often with Western reporters about Islam, and condemned the World Trade Center attacks. "We came here to build, not to destroy," he said in a sermon. "We are the bridge between Americans and one billion Muslims worldwide."He is allegedly linked to Osama Bin Laden: His links to al Qaeda were first suspected by U.S. authorities as long ago as 1999, when the FBI claims he had contact with one of Osama Bin Laden’s "procurement agents."

He had close ties to the 9/11 attackers: Two of the terrorists who hijacked Flight 77 and crashed it into the Pentagon on 9/11 had a “close relationship” with the imam in San Diego and in Washington, D.C. In the Congressional Joint Inquiry on 9/11, al-Awlaki is referred to as one of the terrorist's "spiritual advisor."

Nidal Hasan was a member of his congregation: The Fort Hood shooter — who's reported to view the imam's teachings with "deep respect" — attended the Washington, D.C. mosque where al-Awlaki preached.

The U.K. has censored him: Al-Awlaki was banned from speaking via teleconference at a London event in August 2009 that raised money for Muslims held at Guantánamo Bay.He has written in support of the Fort Hood shootings: Al-Awlaki posted comments on his website in support of the Fort Hood attack, calling Nidal Hasan a "hero" for fighting against "American tyranny."

He was "presumed" killed in a recent U.S.-backed military strike: When the Yemeni military attacked a gathering of al Qaeda leaders in a mountainous province of that country last Dec. 24, officials from Yemen and the U.S. announced that al-Alwaki was believed to have been present and was presumed dead.

Reports of his death may have been premature: Just a few days after the attack, a Yemeni journalist said he'd been contacted by al-Awlaki and that the cleric was alive and well. Al-Awlaki claimed to have been a short distance away from the site of the attack.

His preachings may have inspired the "Underwear Bomber": Investigators in the U.K. think it's possible that Umar Farouk Abdulmutallab was inspired by al-Awlaki's teachings. Specifically, Abdulmutallab was tied to an advocacy group that has "championed" al-Awlaki.

He has been approved for targeted killing: CIA operatives have been given the "extremely rare, if not unprecedented," go-ahead to capture or kill the U.S. citizen, given his danger to America as an al-Qaeda operative.

Faisal Shahzad says al-Awlaki inspired him to act: The man charged with trying to set off a car bomb in Times Square has reportedly told law enforcement that he is a "fan and a follower" of al-Awlaki, and that the influential imam's teachings motivated the attempted bombing.